Urinary stress incontinence affects millions of people, causing discomfort and embarrassment, sometimes to the point of social isolation. Stress incontinence results from weakness or inability of pelvic muscles to hold back urinary flow from the bladder when abdominal pressure increases due to everyday events such as coughing, laughing or mild physical exertion. Muscles involved in controlling the urinary flow include primarily the urethral sphincter and the levator ani, with the cooperation of fibromuscular extensions along the urethra and other muscles in the general region of the pelvic diaphragm. In the United States, it is estimated that 10-13 million patients seek medical care for incontinence each year, of whom about 35% suffer from stress-type incontinence.
Stress incontinence is typically associated with either or both of the following anatomical conditions:                Urethral hypermobility—Weakness of or injury to pelvic floor muscles causes the bladder to descend during abdominal straining or pressure, allowing urine to leak out of the bladder. This is the more common source of stress incontinence.        Intrinsic sphincter deficiency—In this condition, the urethral musculature is unable to completely close the urethra or keep it closed during stress.        
A large variety of products and treatment methods are available for personal and medical care of incontinence. Most patents suffering from mild to moderate incontinence use diapers or disposable absorbent pads. These products are not sufficiently absorbent to be effective in severe cases. They are uncomfortable to wear, and cause skin irritation, as well as unpleasant odors. Other non-surgical products for controlling incontinence include urethral inserts (or plugs) and externally-worn adhesive patches. Drugs are also used in some cases.
Various surgical procedures have been developed for bladder neck suspension, primarily to control urethral hypermobility by elevating the bladder neck and urethra. These procedures typically use bone anchors and sutures or slings to support the bladder neck. The success rates for bladder neck suspension surgery in controlling urinary leakage are typically in the 60-80% range, depending on the patient's condition, the surgeon and the procedure that is used. The disadvantages of surgery are its high cost, need for hospitalization and long recovery period, and high frequency of complications.
For serious cases of intrinsic sphincter deficiency, artificial urinary sphincters have been developed. For example, the AMS 800 urinary sphincter, produced by American Medical Systems Inc., of Minnetonka, Minn., includes a periurethral inflatable cuff, used to overcome urinary incontinence when the function of the natural sphincter is impaired. The cuff is coupled to a manually-operated pump and a pressure regulator chamber, which are implanted in a patient's body together with the cuff. The cuff is maintained at a constant pressure of 60-80 cm of water, which is generally higher than the bladder pressure. To urinate, the patient releases the pressure in the cuff by pressing on the implanted pump, which pumps the fluid out of the cuff to the chamber. Aspects of this system are described in U.S. Pat. No. 4,222,377, whose disclosure is incorporated herein by reference.
This artificial sphincter has several shortcomings, however. The constant concentric pressure that the peripheral cuff exerts on the urethra results in impaired blood supply to tissue in the area, leading to tissue atrophy, urethral erosion and infection. Furthermore, the constant pressure in the cuff is not always sufficient to overcome transient increases in bladder pressure that may result from straining, coughing, laughing or contraction of the detrusor muscle, for example. In such cases, urine leakage may result.
U.S. Pat. Nos. 4,571,749 and 4,731,083, whose disclosures are incorporated herein by reference, describe an artificial sphincter device whose pressure can vary in response to changes in abdominal or intravesical (bladder) pressure. The device includes a periurethral cuff with subdermal pump and pressure regulator, with the addition of a hydraulic pressure sensor. This system is complicated, however, and requires manual manipulation of the subdermal pump and cuff control.
Medtronic Neurological, of Columbia Heights, Minn., produces a device known as Interstim for treatment of urge incontinence, which is a different disorder from stress incontinence. In urge incontinence, a sudden, urgent need to pass urine causes involuntary urination, before the patient can get to a toilet. The condition may be caused by damage to nerve pathways from the brain to the bladder or by psychosomatic factors, leading to involuntary bladder contraction. Interstim uses an implantable pulse generator, which is surgically implanted in the lower abdomen and wired to nerves near the sacrum (the bone at the base of the spine) in a major surgical procedure under general anesthesia. Electrical impulses are then transmitted continuously to a sacral nerve that controls urinary voiding. The continuous electrical stimulation of the nerve has been found to reduce or eliminate urge incontinence in some patients.
Exercise and behavioral training are also effective in some cases in rehabilitating pelvic muscles and thus reducing or resolving incontinence. Patients are taught to perform Kegel exercises to strengthen their pelvic muscles, which may be combined with electrical stimulation of the pelvic floor. Electromyographic biofeedback may also be provided to give the patients an indication as to the effectiveness of their muscular exertions. Retraining muscles is not possible or fully effective for most patients, however, particularly when there may be neurological damage or other pathologies involved.
U.S. Pat. No. 3,628,538, whose disclosure is incorporated herein by reference, describes apparatus for stimulating a muscle, using an electromyogram (EMG) signal sensed in the muscle. If the signal is greater than a predetermined threshold value, a stimulator circuit applies a voltage to electrodes adjacent to the muscle. The apparatus is said to be particularly useful in overcoming incontinence.
Various types of electrodes have been proposed for applying electrical stimulation to pelvic muscles so as to prevent unwanted urine flow through the urethra. For example, U.S. Pat. No. 5,562,717 describes electrodes that are placed on the body surface, typically in the areas of the porineum and the sacrum, and are electrically actuated to control incontinence. U.S. Pat. No. 4,785,828 describes a vaginal plug having electrodes on an outer surface thereof. A pulse generator in the plug applies electrical pulses to the electrodes so as to constrict the pelvic muscles and prevent urine flow. U.S. Pat. No. 4,153,059 describes an intra-anal electrode, to which repetitive electrical pulses are applied in order to control urinary incontinence. U.S. Pat. No. 4,106,511 similarly describes an electrical stimulator in the form of a plug for insertion into the vagina or the anus. U.S. Pat. No. 3,666,613 describes a pessary ring having two electrodes thereon, which are energized to control incontinence. The disclosures of all of the above-mentioned patents are incorporated herein by reference.
U.S. Pat. No. 4,580,578, whose disclosure is also incorporated herein by reference, describes a device for stimulating the sphincter muscles controlling the bladder. A supporting body is fitted into the patient's vulva between the labia, so that two electrodes attached to the supporting body contact the epidermal surface on either side of the external urethral orifice. Electrical impulses are applied to the electrodes to stimulate the region of the sphincter.